This invention relates to methods for processing waste materials, and in particular, to methods for converting waste materials into a glass.
Large quantities of highly radioactive acid solution have been produced during the processing of radioactive materials. The acid solution was neutralized with sodium hydroxide and stored in tanks for treatment at some later time. Over many years the quantities of such neutralized hazardous waste have grown to very large sizes. The waste itself is highly variable, due to mixing of materials from various processing operations and changes in reprocessing technology over a period of many years.
The waste material includes high-pH sludges and supernatant liquids containing sodium nitrate and hydroxide, formed from neutralization of nitric acid fuel dissolution liquors. Sodium nitrite is also present as a corrosion inhibitor. The sludge layer is viscous and sticky, and contains large quantities of aluminum and iron, along with transuranic species and fission products, with plutonium, technetium, .sup.90 Sr, and .sup.137 Cs being four species of primary concern. Large quantities of rare earth fluorides or bismuth phosphate may also be found in the sludge layer. The supernatant phase also contains a large variety of other salts, including halides, sulfate, carbonate, phosphate, ferrocyanide, and various organic species.
Vitrification is currently the technology of choice for the disposal of high-level nuclear waste (HLW). Typical vitrification processes such as the use of submerged electrode resistance-heated pot melters, require long residence time to complete the glassforming process. Low-level waste has been converted into concrete-like material known as grout, by the addition of cementaceous material to a low-activity waste solution.
Vitrification would also be appropriate for the disposal of low-level waste (LLW). However, the volume of low-level waste is significantly greater than the volume of HLW. Scaling up such conventional vitrification processes would require very large equipment to process large volumes of waste. It would be desirable to have a waste vitrification process that can process large volumes of radioactive and hazardous waste material.